Greyscale lithography techniques for manufacturing field plates

Abstract

Methods for efficiently manufacturing field plates with one or more sloped profiles are described. The fabrication of a field plate structure may include the application of greyscale lithography techniques to enable the concurrent formation of one or more sloped surfaces of the field plate structure during one or more common processing steps. A technical benefit of manufacturing field plate structures that have one or more sloped surfaces using greyscale lithography is that fabrication costs may be substantially reduced by reducing the number of process steps required to form the field plate structures.

What is claimed is: 
     
       1. A method, comprising:
 forming a drain electrode above a substrate; 
 depositing a passivation layer above the drain electrode; 
 depositing a layer of photoresist above the passivation layer; 
 forming a slanted photoresist profile within the layer of photoresist using greyscale lithography; 
 etching at least a portion of the passivation layer to transfer the slanted photoresist profile from the layer of photoresist to the passivation layer, the etched portion of the passivation layer includes a slope that extends in a direction of the drain electrode such that a thickness of the passivation layer under the slope increases as the slope gets closer to the drain electrode; 
 depositing one or more conducting layers above the etched portion of the passivation layer; and 
 etching at least a portion of the one or more conducting layers, the etching the at least the portion of the one or more conducting layers includes etching the one or more conducting layers to concurrently form a source-connected field plate and a gate-connected field plate. 
 
     
     
       2. The method of  claim 1 , wherein:
 the etching the at least the portion of the passivation layer to transfer the slanted photoresist profile from the layer of photoresist to the passivation layer includes performing reactive-ion etching to transfer the slanted photoresist profile from the layer of photoresist to the passivation layer. 
 
     
     
       3. The method of  claim 1 , further comprising:
 forming a source electrode above the substrate; and 
 forming a source connection connecting the source electrode to the source-connected field plate. 
 
     
     
       4. The method of  claim 1 , further comprising:
 forming a gate electrode above the substrate; and 
 the depositing the one or more conducting layers above the etched portion of the passivation layer includes depositing the one or more conducting layers over the gate electrode. 
 
     
     
       5. A method for fabricating field plate structures, comprising:
 forming a source electrode; 
 depositing a dielectric layer above an electrode; 
 depositing a layer of photoresist above the dielectric layer; 
 forming a profile within the layer of photoresist using greyscale lithography, the profile includes a first slope associated with a field plate; 
 etching a portion of the dielectric layer to transfer the profile from the layer of photoresist to the dielectric layer, the etched portion of the dielectric layer includes a slope corresponding to the first slope that extends in a direction of the electrode such that a thickness of the dielectric layer under the slope increases as the slope gets closer to the electrode; 
 depositing one or more conducting layers above the etched portion of the dielectric layer; 
 etching the one or more conducting layers to form the field plate; and 
 forming a source connection connecting the source electrode to the field plate, a portion of the source connection is formed on a different insulating layer from the field plate. 
 
     
     
       6. The method of  claim 5 , further comprising:
 forming a gate electrode; and 
 the depositing the one or more conducting layers above the etched portion of the dielectric layer includes depositing the one or more conducting layers over the gate electrode. 
 
     
     
       7. The method of  claim 5 , wherein:
 the electrode comprises a drain electrode. 
 
     
     
       8. The method of  claim 5 , wherein:
 the forming the profile includes exposing the layer of photoresist to light and then removing a portion of the layer of photoresist to form the profile. 
 
     
     
       9. A method for fabricating a field plate, comprising:
 forming an electrode above a surface; 
 forming a source electrode above the surface; 
 depositing a dielectric layer above the electrode; 
 depositing a layer of photoresist above the dielectric layer; 
 forming a profile within the layer of photoresist using greyscale lithography, the profile includes a first slope associated with the field plate; 
 etching a portion of the dielectric layer to transfer the profile from the layer of photoresist to the dielectric layer, the etched portion of the dielectric layer includes a slope corresponding to the first slope that extends in a direction of the electrode such that a thickness of the dielectric layer under the slope increases as the slope gets closer to the electrode; 
 depositing one or more conducting layers above the etched portion of the dielectric layer to form the field plate; and 
 forming a source connection connecting the source electrode to the field plate, a portion of the source connection is formed on a different insulating layer from the field plate. 
 
     
     
       10. The method of  claim 9 , further comprising:
 forming a gate electrode above the surface; and 
 the depositing the one or more conducting layers above the etched portion of the dielectric layer includes depositing the one or more conducting layers over the gate electrode. 
 
     
     
       11. The method of  claim 9 , wherein:
 the electrode comprises a drain electrode.